Beamlines | I11 Case Study
Complex metal hydrides show promise for hydrogen storage
Combinatorial high-throughput screening at Diamond may prove useful in discovering novel bulk hydrogen storage materials, according to new research published this month in the Royal Society of Chemistry’s Faraday Discussions journal.
A team of researchers from the ‘HyStorM’ project, a collaboration between Oxford University, Johnson Matthey, Ilika Technologies and the ISIS facility, funded by the Technology Strategy Board, used innovative high-resolution Powder X-Ray Diffraction (XRD) techniques on Diamond’s I11 beamline to examine the hydrogen storage properties of a range of metal borohydrides. These experiments have included the first ever high temperature high hydrogen pressure diffraction experiments at Diamond.
Metal boron hydrides are promising as hydrogen fuel storage media, as they have high energy density by volume and weight. However, because they bind hydrogen very strongly, high temperatures, typically greater than 100- 200°C are required to release the hydrogen. This energy cost can be reduced by reacting them with alloys or complex hydrides of sodium, lithium, calcium, titanium, aluminium and boron.
The goal of the the ‘HyStorM’ partners is to identify materials that can store and release hydrogen in an energy-efficient reversible system that can be used in onboard hydrogen fuel systems, with temperature and pressure parameters <100°C for release and <700 bar for recharge (20-60 kJ/mol).
Their paper, ‘A multidisciplinary combinatorial approach for tuning promising hydrogen storage materials towards automotive applications’ reports on results within the ternary compositions Mg–Ti–B and Ca–Ti–B, and demonstrates how using a combination of high-throughput combinatorial thin-film synthesis, bulk powder synthesis and XRD at Diamond has led to novel insights.
Professor Bill David of STFC and the University of Oxford’s inorganic chemistry laboratory led the experiments at Diamond.
“We were hoping to be able to determine the crucial structural parameters that affect the temperatures of decomposition and rehydrogenation of these high hydrogen density materials. Our studies have shown that we can influence the decomposition temperature and rehydrogenation processes by careful control of the decomposition mechanisms.”
Prof Bill David
Unique high-throughput combinatorial thin-film technologies are used to screen materials' hydrogen storage properties. Promisingly, thin-film work on Mg–Ti–B identified a high capacity hotspot corresponding to Mg0.36Ti0.06B0.58, with 10.6 wt% H2 capacity, showing tuned storage properties indicative of mixed metal borohydride type film material, although the thin-film Ca–Ti–B ternary showed only low hydrogen storage capacities. In the bulk, Ti-doping experiments on Ca(BH4)2 demonstrated reversible storage capacities up to 5.9 wt% H2.
Further characterisation experiments are required to decipher the role of the Ti-dopant in these systems in both films and in the bulk, and we can look forward to further developments in the months ahead.
A multidisciplinary combinatorial approach for tuning promising hydrogen storage materials towards automotive applications, Faraday Discussions 13 May 2011
DOI: 10.1039/C0FD00018C
